The embryo grading process begins after oocyte (egg) recovery. At this stage, eggs are placed into an incubator with controlled levels of carbon dioxide, oxygen, and nitrogen for several hours, after which an embryologist takes the eggs from the incubator, removes the cumulus cells surrounding them, and checks them for maturity. Mature eggs undergo intracytoplasmic sperm injection (ICSI) and are placed back in the incubator. It is important that only mature eggs undergo ICSI, as immature eggs may fertilize when injected with sperm but may not produce a viable ongoing pregnancy. Once an egg undergoes ICSI and is fertilized by sperm, it is called an embryo.
On the first day, after insemination, the embryos are checked for fertilization but not graded. Embryos are graded at Day 3 and after Day 5, for further developmental evaluation until it reaches the blastocyst stage. This is the developmental stage that occurs prior to implantation of the embryo in the uterus. Blastocyst implantation after day 5 is beneficial because it leads to more viable embryos that have already overcome possible developmental hurdles.
If the embryos were cultured to blastocyst after day 5 the goal becomes evaluating each embryo for optimal blastocyst development for a successful IVF. Preimplantation genetic test can also be done at the blastocyst stage. Embryos that aren’t chosen for transfer will be evaluated to see if they’re suitable for cryopreservation for possible future use.
New Hope Fertility Center has been in the news as a leader in using abnormal embryos for in vitro fertilization transfers because we understand that the few cells that are biopsied might not be indicative of an unhealthy embryo.
It’s important to note that embryo grading is a subjective process. An embryologist makes an assumption about an egg or embryo’s maturity and potential viability based on their own experience and expertise, but there is no clear cut way to evaluate whether an embryo will result in a successful pregnancy.